Claim CD011.6:

Coal and oil are supposedly millions of years old. Effectively all of the
carbon-14 in a sample would have decayed in that time. But carbon-14
still exists in coal, implying an age of only about 50,000 years.

Response:

New 14C is formed from background radiation, such as
radioactivity in the surrounding rocks. In some cases, 14C
from the atmosphere can contaminate a sample. A few processes that can
add "modern" 14C to coal are:

Sulfur bacteria, which commonly grow in coal.

Secondary carbonates from groundwater that form on fracture
surfaces.

Whewellite, a carbon-containing mineral, that often forms as coal
weathers.

Minute amounts of contamination from these sources can cause apparent
ages around 50,000 years, which is near the limit of the maximum age
that carbon dating can measure.